Glomerular Filtration Rate (GFR) Calculator (CKD-EPI Creatinine 2021)
Estimated GFR:
Understanding Glomerular Filtration Rate (GFR)
The Glomerular Filtration Rate (GFR) is a crucial test that indicates how well your kidneys are functioning. It measures the amount of blood that your kidneys filter every minute. Kidneys are responsible for removing waste products and excess fluid from your blood. The GFR is considered the best overall index of kidney function.
As kidney disease progresses, the GFR typically declines. Measuring GFR helps doctors diagnose kidney disease, monitor its progression, and adjust treatment plans. A normal GFR varies with age, but in general, a higher GFR indicates better kidney function.
What are the Stages of Chronic Kidney Disease (CKD) based on GFR?
Chronic Kidney Disease (CKD) is typically staged based on GFR values. These stages help healthcare providers understand the severity of kidney damage and guide treatment decisions:
- Stage 1: GFR of 90 or higher with other signs of kidney damage (e.g., protein in urine). Normal or high GFR.
- Stage 2: GFR between 60 and 89 with other signs of kidney damage. Mildly decreased GFR.
- Stage 3a: GFR between 45 and 59. Mildly to moderately decreased GFR.
- Stage 3b: GFR between 30 and 44. Moderately to severely decreased GFR.
- Stage 4: GFR between 15 and 29. Severely decreased GFR.
- Stage 5: GFR less than 15. Kidney failure.
The CKD-EPI Creatinine 2021 Equation
The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) Creatinine 2021 equation is a widely used formula to estimate GFR. It is considered more accurate than previous equations and accounts for serum creatinine levels, age, sex, and race.
The equation is as follows:
GFR = 142 × min(Scr/κ, 1)^α × max(1 – 0.009 × Age) × 1.012^Sex × 1.159^Race
Where:
- Scr is serum creatinine in mg/dL.
- κ is 0.7 for females and 0.9 for males.
- α is -0.329 for females and -0.411 for males.
- min indicates the minimum of Scr/κ or 1.
- max indicates the maximum of 1 – 0.009 × Age or 0.966.
- Sex is 1 for females and 0 for males.
- Race is 1.159 for Black or African American individuals and 1 for White, Other individuals.
This calculator uses the CKD-EPI 2021 equation to provide an estimated GFR. It is important to note that this is an estimation, and your doctor will use this result along with other clinical information to assess your kidney health.
Example Calculation:
Let's consider a 65-year-old Black female with a serum creatinine of 1.2 mg/dL.
- Serum Creatinine (Scr) = 1.2 mg/dL
- Age = 65 years
- Gender = Female
- Race = Black
For a female: κ = 0.7, α = -0.329, Sex = 1, Race = 1.159.
First, calculate Scr/κ: 1.2 / 0.7 = 1.714. Since 1.714 is greater than 1, min(Scr/κ, 1) = 1.
Next, calculate max(1 – 0.009 × Age): 1 – (0.009 * 65) = 1 – 0.585 = 0.415. Since 0.415 is less than 0.966, the max function in the original description was a simplification. The CKD-EPI 2021 equation uses a slightly different adjustment for age that is incorporated directly: (1 – 0.009 * (Age – 65)). For age 65, this term is 1.
The 2021 equation uses a simplified form where the age component is (1 – 0.009 * (Age – 65)) if Age > 65, and 1 if Age <= 65. For Age=65, this is 1.
Let's use the standard CKD-EPI 2021 formulation:
GFR = 142 × min(Scr/κ, 1)^α × (1 – 0.009 × (Age – 65)) × 1.012^Sex × 1.159^Race (where (Age – 65) is used if Age > 65, otherwise 1)
For this example (Age=65, Female, Black, Scr=1.2):
- Scr/κ = 1.2 / 0.7 = 1.714
- min(1.714, 1) = 1
- α = -0.329
- (1 – 0.009 * (65 – 65)) = 1
- Sex = 1 (Female)
- Race = 1.159 (Black)
GFR = 142 × (1)^(-0.329) × 1 × 1.012^1 × 1.159^1
GFR = 142 × 1 × 1 × 1.012 × 1.159
GFR ≈ 166.17 mL/min/1.73 m²
This estimated GFR of approximately 166 mL/min/1.73 m² would indicate that the kidneys are functioning very well.